Processes for the manufacture and purification of 1,1,2,2,3,3,4,4-octafluorobutane and by-products

ABSTRACT

A process is disclosed for producing 1,12,2,3,3,4,4-octafluorobutane. The process involves chlorination of 2,2,3,3-tetrafluorobutane to form a mixture of chloro-compounds wherein compounds of the formula C 4  H 4  Cl 6-x  F 4  (where x is 0 or 1) comprise at least 50 mole % of the mixture of chloro-compounds, followed by hydrofluorination, then hydrogenolysis, and sufficient recycle to provide a selectivity to CHF 2  CF 2  CF 2  CHF 2  of at least about 75% based upon the moles of CH 3  CF 2  CF 2  CH 3  reacted. Also disclosed is a multi-distillation process for the purification of CHF 2  CF 2  CF 2  CHF 2  from a mixture of HF and the compound(s). Also disclosed are certain new halogenated butanes containing fluorine, and a composition which contains HF in combination with an effective amount of CHF 2  CF 2  CF 2  CHF 2  to form an azeotrope or azeotrope-like composition with hydrogen fluoride.

This application derives priority from Verified Provisional applicationSer. No. 60/019,993 filed Jun. 18, 1996.

FIELD OF THE INVENTION

This invention relates to the manufacture of1,1,2,2,3,3,4,4-octafluorobutane, its azeotropic compositions withhydrogen fluoride and their use in separation processes.

BACKGROUND

Chlorofluorocarbons (CFCs, i.e., compounds containing only carbon,fluorine and chlorine) have been used for many years as refrigerants,heat transfer media, foam expansion agents, aerosol propellants,solvents, fire extinguishants and power cycle working fluids. Forexample, various CFC solvents have been used as cleaning liquids for theremoval of contaminants from contaminated articles and materials.Certain fluorine-containing organic compounds such as1,1,2-trichloro-1,2,2-trifluoroethane (CFC-113) have been reported asuseful for this purpose, particularly with regard to cleaning organicpolymers and plastics which may be sensitive to other more common andmore powerful solvents such as trichloroethylene or perchloroethylene.Recently, however, there have been efforts to reduce the use of certaincompounds such as trichlorotrifluoroethane which also contain chlorinebecause of a concern over their potential to deplete ozone.Consequently, there is a worldwide effort to find alternative compounds.

The properties of halogenated hydrocarbons can be influenced by thearrangement of the halogens (and hydrogen, when present) on the carbonframework. One of the challenges in preparing compounds containingfluorine and hydrogen has been to achieve the desired arrangement ofsuch substituents. When more than one hydrogen is present in themolecule, one arrangement involves providing a hydrogen on differentcarbons spaced a selected distance from one another along a carbonchain. For example, in a compound of the formula C₄ H₂ F₈, it can bedesirable to provide a hydrogen substituent on each of two carbon atomswhich are separated from one another by a chain of two other carbonatoms. 1,1,2,2,3,3,4,4-Octafluorobutane (i.e., CHF₂ CF₂ CF₂ CHF₂ orHFC-338pcc) is such a compound. HFC-338pcc forms useful blends, andparticularly azeotropes, with solvents such as alcohols, ketones, andother halogenated solvents to form compositions useful for cleaningsurfaces, especially electronic components as disclosed in U.S. Pat.Nos. 5,250,208, 5,221,493 and 5,194,170. There is a need fornon-chlorinated solvents like HFC-338pcc (which have little effect onthe ozone layer) as replacements for more chlorinated solvents such asCFC-113.

SUMMARY OF THE INVENTION

A process is provided for producing 1,1,2,2,3,3,4,4-octafluorobutane(i.e., CHF₂ CF₂ CF₂ CHF₂ or HFC-338pcc). The process comprises (a)reacting a mixture comprising 2,2,3,3-tetrafluorobutane (i.e., CH₃ CF₂CF₂ CH₃ or HFC-374scc) and chlorine to form a mixture ofchloro-compounds selected from the group consisting of CCl₃ (CF₂)₂ CCl₃(CFC-314jcc), CHCl₂ (CF₂)₂ CCl₃ (HCFC-324jcc), CH₂ Cl(CF₂)₂ CCl₃(HCFC-334jcc), CH₃ (CF₂)₂ CCl₃ (HCFC-344jcc), CH₃ (CF₂)₂ CHCl₂(HCFC-354ncc) and CH₃ (CF₂)₂ CH₂ Cl (HCFC-364occ) wherein compounds ofthe formula C₄ H_(x) Cl_(6-x) F₄ (where x is 0 or 1) comprise at leastabout 50 mole % of said mixture of chloro-compounds; (b) contacting amixture comprising compounds of the formula C₄ H_(x) Cl_(6-x) F₄ from(a) and hydrogen fluoride (HF) with a fluorination catalyst to form amixture of fluoro-compounds selected from the group consisting of CCl₂F(CF₂)₂ CCl₃, CCl₂ F(CF₂)₂ CCl₂ F, CCl₂ F(CF₂)₂ CClF₂, CClF₂ (CF₂)₂CClF₂, CClF₂ (CF₂)₂ CF₃, CHCl₂ (CF₂)₂ CCl₂ F, CHClF(CF₂)₂ CCl₃, CHCl₂(CF₂)₂ CClF₂, CHClF(CF₂)₂ CCl₂ F, CHF₂ (CF₂)₂ CCl₃, CHClF(CF₂)₂ CClF₂,CHF₂ (CF₂)₂ CCl₂ F, CHCl₂ (CF₂)₂ CF₃, CHClF(CF₂)₂ CF₃, CHF₂ (CF₂)₂ CClF₂and CHF₂ (CF₂)₂ CF₃ wherein compounds of the formula C₄ H_(2-y) Cl_(y)F₈ (where y is 1 or 2) comprise at least about 10 mole % of said mixtureof fluoro-compounds; and (c) contacting a mixture comprising compoundsof the formula C₄ H_(2-y) Cl_(y) F₈ from (b) and hydrogen with ahydrogenolysis catalyst to produce CHF₂ CF₂ CF₂ CHF₂. Sufficientchloro-compounds formed in (a) are recycled to the chlorination of (a)and sufficient fluoro-compounds formed in (b) are recycled to thechlorination of (a) or the fluorination of (b) to provide a selectivityto CHF₂ CF₂ CF₂ CHF₂ of at least about 75% based upon the moles of CH₃CF₂ CF₂ CH₃ reacted in (a).

This invention also provides a process for the purification of at leastone compound selected from the group consisting of CCl₂ F(CF₂)₂ CCl₃,CCl₂ F(CF₂)₂ CCl₂ F, CCl₂ F(CF₂)₂ CClF₂, CClF₂ (CF₂)₂ CClF₂, CClF₂(CF₂)₂ CF₃, CHCl₂ (CF₂)₂ CCl₂ F, CHClF(CF₂)₂ CCl₃, CHCl₂ (CF₂)₂ CClF₂,CHClF(CF₂)₂ CCl₂ F, CHF₂ (CF₂)₂ CCl₃, CHClF(CF₂)₂ CClF₂, CHF₂ (CF₂)₂CCl₂ F, CHCl₂ (CF₂)₂ CF₃, CHClF(CF₂)₂ CF₃, CHF₂ (CF₂)₂ CClF₂, CHF₂ CF₂CF₂ CHF₂, CHF₂ CF₂ CF₂ CH₂ F, CHF₂ CF₂ CF₂ CF₃ and CH₂ FCF₂ CF₂ CF₃ froma mixture comprising HF and said at least one compound. The purificationprocess comprises (a) subjecting the mixture of HF and said at least onecompound to a distillation step in which a composition enriched ineither (i) HF or (ii) said at least one compound is removed as a firstdistillate with the bottoms being enriched in the other of saidcomponents (i) or (ii); (b) subjecting said first distillate to anadditional distillation conducted at a different pressure in which thecomponent enriched as bottoms in (a) is removed as a second distillatewith the bottoms of the additional distillation enriched in thecomponents enriched in the first distillate; and (c) recovering said atleast one compound essentially free of HF as bottoms from either thedistillation of (a) or the distillation of (b).

New compounds provided in accordance with this invention include CCl₂FCF₂ CF₂ CClF₂, CCl₃ CF₂ CF₂ CCl₂ F, CHCl₂ CF₂ CF₂ CCl₃, CHCl₂ CF₂ CF₂CCl₂ F, CHClFCF₂ CF₂ CCl₃, CHCl₂ CF₂ CF₂ CClF₂, CHClFCF₂ CF₂ CCl₂ F,CHF₂ CF₂ CF₂ CCl₃, CHF₂ CF₂ CF₂ CCl₂ F, CHClFCF₂ CF₂ CF₃, CH₃ CF₂ CF₂CH₂ Cl and CH₂ ClCF₂ CF₂ CCl₃. These compounds are useful asintermediates for producing hydrofluorocarbons.

Also provided are compositions which comprise hydrogen fluoride incombination with an effective amount of CHF₂ CF₂ CF₂ CHF₂ to form anazeotrope or azeotrope-like composition with hydrogen fluoride, saidcomposition containing from about 3.5 to 36.8 mole percent CHF₂ CF₂ CF₂CHF₂.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a schematic flow diagram of an embodiment of the purificationprocess of this invention, namely an azeotrope separation process.

DETAILED DESCRIPTION

The present invention includes a process for the separation of anazeotropic mixture of hydrogen fluoride (HF) and1,1,2,2,3,3,4,4-octafluorobutane (i.e., CHF₂ CF₂ CF₂ CHF₂ or HFC-338pcc)to obtain CHF₂ CF₂ CF₂ CHF₂ essentially free of HF. For example, (a) aninitial mixture wherein the molar ratio of HF to HFC-338pcc is greaterthan about 3:1 can be separated by azeotropic distillation in a firstdistillation column wherein the temperature of the feed inlet to saiddistillation column is about 102° C. and the pressure is about 216 psia(1490 kPa), with azeotrope products containing HF and HFC-338pcc beingremoved as distillate from the top of the first distillation column andHF being removed from the bottom of the first distillation column; (b)said azeotrope products from the top of the column in step (a) can befed to a second distillation column wherein the temperature of the feedinlet to said second distillation column is about 41° C. and thepressure is about 21.2 psia (146 kPa), with azeotrope productscontaining HF and HFC-338pcc being removed as distillate from the top ofthe second distillation column; and (c) essentially pure HFC-338pcc canbe recovered from the bottom of the second distillation column in step(b). Optionally, said azeotrope products containing HF and HFC-338pccremoved from the top of the second distillation column can be recycledas feed to step (a).

In another embodiment of this invention, (a) an initial mixture whereinthe molar ratio of HF to HFC-338pcc is about 3:1 or less, can beseparated by azeotropic distillation in a first distillation columnwherein the temperature of the feed inlet to said distillation column isabout 41° C. and the pressure is about 21.2 psia (146 kPa) withazeotrope products containing HF and HFC-338pcc being removed asdistillate from the top of the first distillation column; (b) saidazeotrope products from the top of the column in step (a) can be fed toa second distillation column wherein the temperature of the feed inletto said second distillation column is about 101° C. and the pressure isabout 216 psia (1490 kPa), with azeotrope products containing HF andHFC-338pcc being removed as distillate from the top of the seconddistillation column and HF being removed from the bottom of the seconddistillation column; and (c) essentially pure HFC-338pcc can berecovered from the bottom of the first distillation column. Optionally,said azeotrope products containing HF and HFC-338pcc from the top of thesecond distillation column can be recycled as feed to step (a).

The above embodiments of this invention involve azeotropic distillationof mixtures of HF and CHF₂ CF₂ CF₂ CHF₂ (HFC-338pcc). The productmixtures distilled in accordance with this invention can be obtainedfrom a variety of sources. These sources include product mixtures fromthe following sequence of reactions.

CH₃ CF₂ CF₂ CH₃ (HFC-374scc), a compound known in the art, can becontacted with chlorine (e.g., in the vapor phase) in the presence of achlorination catalyst. The catalyst for the chlorination may be composedof activated carbon alone or carbon with a chloride and/or fluoride of ametal selected from the group consisting of zinc, copper, chromium,ruthenium, rhodium, platinum and mixtures thereof. Under reactionconditions the metal halides may be in the form of mixed metal halides(e.g., a chlorofluoride). Additional details for the catalyticchlorination of a hydrofluorocarbon such as HFC-374scc are disclosed inU.S. Pat. No. 5,120,883. Alternatively, HFC-374scc may be chlorinated inthe liquid phase in the presence of a source of ultraviolet radiationand optionally in the presence of a solvent. Such a technique is wellknown in the art; see for example, the article by Poustma in "FreeRadicals" (Wiley: New York, 1973), J. K. Kochi, ed., pp. 159-229.

The chlorination may be run such that products of this chlorinationreaction consist essentially of CCl₃ CF₂ CF₂ CCl₃ (CFC-314jcc), CHCl₂CF₂ CF₂ CCl₃ (HCFC-324jcc) and HCl. For example, at least 6 moles ofchlorine can be contacted with HFC-374scc for a time sufficient to yieldproducts consisting essentially of CFC-314jcc and HCFC-324jcc.HCFC-324jcc is a new composition of matter. Intermediates produced inthe chlorination of CH₃ CF₂ CF₂ CH₃ include CH₃ CF₂ CF₂ CH₂ Cl, CH₃ CF₂CF₂ CHCl₂, CH₃ CF₂ CF₂ CCl₃, and CH₂ ClCF₂ CF₂ CCl₃. Said intermediatesare generally lower boiling than CCl₃ CF₂ CF₂ CCl₃ (CFC-314jcc) andCHCl₂ CF₂ CF₂ CCl₃ (HCFC-324jcc) and can be separated therefrom bydistillation and can be recycled to the chlorination reactor. Among thechlorination intermediates, CH₃ CF₂ CF₂ CH₂ Cl (HCFC-364occ) and CH₂ClCF₂ CF₂ CCl₃ (HCFC-334jcc) are new compositions of matter. The mixtureof CFC-314jcc and HCFC-324jcc is contacted with at least astoichiometric amount of HF, based on the moles of CFC-314jcc, in thegaseous phase in the presence of vapor phase fluorination catalysts(preferably after removal of HCl).

Vapor phase fluorination catalysts which may be used include metaloxides and/or other metal salts which are either supported orunsupported. Suitable supports include fluorided alumina, aluminumfluoride and carbon. Catalysts comprising trivalent chromium eithersupported or unsupported are preferred. Other preferred catalysts aremetal halides supported on either fluorided alumina, aluminum fluorideor carbon. The preferred metal halides include those derived fromcobalt, nickel, magnesium and copper. Combinations of metal compoundssuch as those derived from Cr and Mg, Cr and Zn, Cr and Co, and Cr andNi can also be used advantageously. Preferably, when used with asupport, the total metal content of the catalyst will be from about 0.1to 20 percent by weight; typically, from about 0.1 to 10 percent byweight.

Fluorided alumina and aluminum fluoride can be prepared as described inU.S. Pat. No. 4,902,838. Metal halides on aluminum fluoride and metalhalides on fluorided alumina can be prepared by procedures described inU.S. Pat. No. 4,766,260. Catalysts comprising chromium are well known inthe art (see e.g., U.S. Pat. No. 5,036,036). Chromium supported onalumina can be prepared as described in U.S. Pat. No. 3,541,165.Chromium supported on carbon can be prepared as described in U.S. Pat.No. 3,632,834. Catalysts comprising chromium and magnesium may beprepared as described in Canadian Patent No. 2,025,145. Other supportedmetal halides can be prepared in a similar manner to those disclosed inthe above patents.

The fluorination reactor products can include CCl₂ FCF₂ CF₂ CCl₃(CFC-315jcc), CCl₂ FCF₂ CF₂ CCl₂ F (CFC-316kcc), CCl₂ FCF₂ CF₂ CClF₂(CFC-317lcc), CClF₂ CF₂ CF₂ CClF₂ (CFC-318lcc), CClF₂ CF₂ CF₂ CF₃(CFC-319l), CHCl₂ CF₂ CF₂ CCl₂ F (HCFC-325kcc), CHClFCF₂ CF₂ CCl₃(HCFC-325jcc), CHCl₂ CF₂ CF₂ CClF₂ (HCFC-326lcc), CHClFCF₂ CF₂ CCl₂ F(HCFC-326kcc), CHF₂ CF₂ CF₂ CCl₃ (HCFC-326jcc), CHF₂ CF₂ CF₂ CCl₂ F(HCFC-327kcc), CHClFCF₂ CF₂ CClF₂ (HCFC-327lcc), CHCl₂ CF₂ CF₂ CF₃(HCFC-327n), CHF₂ CF₂ CF₂ CClF₂ (HCFC-328lcc), CHClFCF₂ CF₂ CF₃(HCFC-328r), CHF₂ CF₂ CF₂ CF₃ (HFC-329p), HCl and HF. Higher boilingproducts such as CFC-315jcc, CFC-316kcc, HCFC-325kcc, HCFC-325jcc,HCFC-326lcc, HCFC-326kcc, and HCFC-326jcc can be separated from theother fluorination reactor products (e.g., by distillation) and recycledto the fluorination reactor or to the chlorination reactor. Thefluorination reactor product mixture, optionally containing HF, iscontacted with hydrogen in the presence of a hydrogenolysis catalyst,preferably, after removal of HCl. The hydrogenolysis of (c) can be donein the vapor phase over a Group VIII metal catalyst, preferablypalladium, rhodium or ruthenium. Pd and Rh are the more preferredmetals, with palladium being most preferred. The metal catalyst may besupported (e.g., on carbon, alumina, aluminum fluoride, fluoridedalumina or chromium oxide). CHF₂ CF₂ CF₂ CH₂ F, CHF₂ CF₂ CF₂ CF₃, andCH₂ FCF₂ CF₂ CF₃ are typical by-products of (c).

Among the fluorination products, CCl₂ FCF₂ CF₂ CClF₂, CCl₃ CF₂ CF₂ CCl₂F, CHCl₂ CF₂ CF₂ CCl₂ F, CHClFCF₂ CF₂ CCl₃, CHCl₂ CF₂ CF₂ CClF₂,CHClFCF₂ CF₂ CCl₂ F, CHF₂ CF₂ CF₂ CCl₃, CHF₂ CF₂ CF₂ CCl₂ F, andCHClFCF₂ CF₂ CF₃ are new compositions of matter.

Of note are embodiments where CClF₂ CF₂ CF₂ CF₃, CClF₂ CF₂ CF₂ CClF₂,CCl₂ FCF₂ CF₂ CClF₂, CHF₂ CF₂ CF₂ CClF₂, CHClFCF₂ CF₂ CF₃, CHClCF₂ CF₂CClF₂, CHF₂ CF₂ CF₂ CCl₂ F, CHCl₂ CF₂ CF₂ CF₃ and CHF₂ CF₂ CF₂ CF₃ from(b) are all fed to (c). The hydrogenolysis reactor effluent thentypically includes CHF₂ CF₂ CF₂ CHF₂ (HFC-338pcc), HF, HCl and muchlesser amounts of CH₂ FCF₂ CF₂ CHF₂ (HFC-347pcc), CHF₂ CF₂ CF₂ CF₃(HFC-329p), CH₃ CF₂ CF₂ CF₃ (HFC-347s) and CH₂ FCF₂ CF₂ CF₃ (HFC-338q).Typically the selectivity to HFC-338pcc is at least 80%, preferably, atleast 90% based upon the moles of HFC-374scc reacted.

Among the compounds produced during the preparation of HFC-338pcc fromHFC-374scc by the process described above which are likely to formazeotropes with HF are CCl₂ FCF₂ CF₂ CClF₂ (CFC-317lcc), CClF₂ CF₂ CF₂CClF₂ (CFC-318lcc), CClF₂ CF₂ CF₂ CF₃ (CFC-319l), CHClFCF₂ CF₂ CClF₂(HCFC-327lcc), CHF₂ CF₂ CF₂ CClF₂ (HCFC-328lcc), CHClFCF₂ CF₂ CF₃(HCFC-328r), CHF₂ CF₂ CF₂ CF₃ (HFC-329p), CH₂ FCF₂ CF₂ CF₃ (HFC-338q),CH₃ CF₂ CF₂ CF₃ (HFC-347s) and CH₂ FCF₂ CF₂ CHF₂ (HFC-347pcc).Conventional decantation/distillation may be employed if furtherpurification of the listed compounds is desired.

Moreover, a process for purification as provided herein may also beused. Hydrofluoroalkanes and chloro-precursors thereof are provided inthe process for producing HFC-338pcc described above. Typically, thesecompounds as well as HFC-388pcc form azeotropes with HF, and the processfor purification provided herein may be advantageously used forpurification of these compunds from their HF azeotropes (e.g., a binaryazeotrope of HFC-338pcc with HF). Examples of compounds which can bepurified from their binary with HF by this purification process includecompounds selected from the group consisting of CHF₂ CF₂ CF₂ CHF₂, CCl₂FCF₂ CF₂ CClF₂, CClF₂ CF₂ CF₂ CClF₂, CClF₂ CF₂ CF₂ CF₃, CHClFCF₂ CF₂CClF₂, CHF₂ CF₂ CF₂ CCl₂ F, CHF₂ CF₂ CF₂ CClF₂, CHClFCF₂ CF₂ CF₃, CHCl₂CF₂ CF₂ CF₃, CHF₂ CF₂ CF₂ CF₃, CH₂ FCF₂ CF₂ CF₃, CH₃ CF₂ CF₂ CF₃ and CH₂FCF₂ CF₂ CHF₂. Of note is a process wherein CHF₂ CF₂ CF₂ CHF₂ ispurified from a mixture which consists essentially of hydrogen fluoridein combination with an effective amount of CHF₂ CF₂ CF₂ CHF₂ to form anazeotrope or azeotrope-like composition with hydrogen fluoride, saidazeotropic composition containing from about 3.5 to 36.8 mole percentCHF₂ CF₂ CF₂ CHF₂. Also of note is a process wherein HF is recoveredfrom a product mixture including CHF₂ CF₂ CF₂ CHF₂ formed by thereaction of CClF₂ CF₂ CF₂ CClF₂ with hydrogen in the presence of HF; andwherein an azeotropic composition consisting essentially of from about96.5 to 63.2 mole percent HF and about from 3.5 to 36.8 mole percentCHF₂ CF₂ CF₂ CHF₂, is recovered and recycled to a reactor for saidreaction of CClF₂ CF₂ CF₂ CClF₂ and hydrogen in the presence of HF.

The present invention also provides compositions which consistessentially of hydrogen fluoride and an effective amount of CHF₂ CF₂ CF₂CHF₂ to form an azeotropic combination with hydrogen fluoride. Byeffective amount is meant an amount which, when combined with HF,results in the formation of an azeotrope or azeotrope-like mixture. Asrecognized in the art, an azeotrope or an azeotrope-like composition isan admixture of two or more different components which, when in liquidform under given pressure, will boil at a substantially constanttemperature, which temperature may be higher or lower than the boilingtemperatures of the individual components, and which will provide avapor composition essentially identical to the liquid compositionundergoing boiling.

An azeotrope is a liquid mixture that exhibits a maximum or minimumboiling point relative to the boiling points of surrounding mixturecompositions. An azeotrope is homogeneous if only one liquid phase ispresent. An azeotrope is heterogeneous if more than one liquid phase ispresent. Regardless, a characteristic of minimum boiling azeotropes isthat the bulk liquid composition is then identical to the vaporcomposition in equilibrium therewith, and distillation is ineffective asa separation technique. For the purpose of this discussion,azeotrope-like composition means a composition which behaves like anazeotrope (i.e., has constant-boiling characteristics or a tendency notto fractionate upon boiling or evaporation). Thus, the composition ofthe vapor formed during boiling or evaporation of such compositions isthe same as or substantially the same as the original liquidcomposition. Hence, during boiling or evaporation, the liquidcomposition, if it changes at all, changes only to a minimal ornegligible extent. This is to be contrasted with non-azeotrope-likecompositions in which during boiling or evaporation, the liquidcomposition changes to a substantial degree.

Accordingly, the essential features of an azeotrope or an azeotrope-likecomposition are that at a given pressure, the boiling point of theliquid composition is fixed and that the composition of the vapor abovethe boiling composition is essentially that of the boiling liquidcomposition (i.e., no fractionation of the components of the liquidcomposition takes place). It is also recognized in the art that both theboiling point and the weight percentages of each component of theazeotropic composition may change when the azeotrope or azeotrope-likeliquid composition is subjected to boiling at different pressures. Thusan azeotrope or an azeotrope-like composition may be defined in terms ofthe unique relationship that exists among components or in terms of thecompositional ranges of the components or in terms of exact weightpercentages of each component of the composition characterized by afixed boiling point at a specified pressure. It is also recognized inthe art that various azeotropic compositions (including their boilingpoints at particular pressures) may be calculated (see, e.g., W.Schotte, Ind. Eng. Chem. Process Des. Dev. 1980, 19, pp 432-439).Experimental identification of azeotropic compositions involving thesame components may be used to confirm the accuracy of such calculationsand/or to modify the calculations for azeotropic compositions at thesame or other temperatures and pressures.

Compositions may be formed which consist essentially of azeotropiccombinations of hydrogen fluoride with CHF₂ CF₂ CF₂ CHF₂. These includea composition consisting essentially of from about 96.5 to about 63.2mole percent HF and from about 3.5 to 36.8 mole percent CHF₂ CF₂ CF₂CHF₂ (which forms an azeotrope boiling at a temperature from betweenabout -40° C. and about 145° C. and a pressure between about 7.3 kPa andabout 4115 kPa).

At atmospheric pressure, the boiling points of hydrofluoric acid andHFC-338pcc are about 19.5° C. and 44.3° C., respectively. However, therelative volatility at 125 kPa (18.1 psia) and 20° C. of HF andHFC-338pcc was found to be nearly 1.0 as 88.4 mole percent HF and 11.6mole percent HFC-338pcc was approached. These data indicate that the useof conventional distillation procedures will not result in theseparation of a substantially pure compound because of the low value ofrelative volatility of the compounds.

To determine the relative volatility of HF with each of HFC-338pcc, theso-called PTx Method was used. In this procedure, the total absolutepressure in a cell of known volume is measured at a constant temperaturefor various known binary compositions. Use of the PTx Method isdescribed in greater detail in "Phase Equilibrium in Process Design",Wiley-Interscience Publisher, 1970, written by Harold R. Null, on pages124 to 126, the entire disclosure of which is hereby incorporated byreference. Samples of the vapor and liquid, or vapor and each of the twoliquid phases under those conditions where two liquid phases exist, wereobtained and analyzed to verify their respective compositions.

These measurements can be reduced to equilibrium vapor and liquidcompositions in the cell by an activity coefficient equation model, suchas the Non-Random, Two-Liquid (NRTL) equation, to represent liquid phasenon-idealities. Use of an activity coefficient equation, such as theNRTL equation, is described in greater detail in "The Properties ofGases and Liquids", 4th Edition, publisher McGraw Hill, written by Reid,Prausnitz and Poling, on pages 241 to 387; and in "Phase Equilibria inChemical Engineering", published by Butterworth Publishers, 1985,written by Stanley M. Walas, pages 165 to 244; the entire disclosure ofeach of the previously identified references are hereby incorporated byreference.

Without wishing to be bound by any theory or explanation, it is believedthat the NRTL equation can sufficiently predict whether or not mixturesof HF and HFC-338pcc behave in an ideal manner, and can sufficientlypredict the relative volatilities of the components in such mixtures.Thus, while HF has a good relative volatility compared to HFC-338pcc atlow HFC-338pcc concentrations, the relative volatility becomes nearly1.0 as 11.6 mole percent HFC-338pcc was approached at 20° C. This wouldmake it impossible to separate HFC-338pcc from HF by conventionaldistillation from such a mixture. Where the relative volatilityapproaches 1.0 defines the system as forming a near-azeotrope. Where therelative volatility is 1.0 defines the system as forming an azeotrope.

It has been found that azeotropes of HF and HFC-338pcc are formed at avariety of temperatures and pressures. At a pressure of 18.1 psia (125kPa) and 20° C., the azeotrope vapor composition was found to be about88.4 mole percent HF and about 11.6 mole percent HFC-338pcc. At apressure of 69.2 psia (477 kPa) and 60° C., the azeotrope vaporcomposition was found to be about 81.6 mole percent HF and 18.4 molepercent HFC-338pcc. Based upon the above findings, it has beencalculated that an azeotropic composition of about 96.5 mole percent HFand about 3.5 mole percent HFC-338pcc can be formed at -40° C. and 1.06psia (7.3 kPa) and an azeotropic composition of about 63.2 mole percentHF and about 36.8 mole percent HFC-338pcc can be formed at 145° C. and597 psia (4115 kPa). Accordingly, the present invention provides anazeotrope or azeotrope-like composition consisting essentially of fromabout 96.5 to 63.2 mole percent HF and from about 3.5 to 36.8 molepercent HFC-338pcc, said composition having a boiling point from about-40° C. at 7.3 kPa to about 145° C. at 4115 kPa.

The HFC-338pcc/HF azeotrope is useful as recycle to the fluorinationreactor, where the recycled HF can function as a reactant and therecycled HFC-338pcc can function to moderate the temperature effect ofthe heat of reaction. It will also be apparent to one of ordinary skillin the art that distillation including azeotropes with HF can typicallybe run under more convenient conditions than distillation without HF,e.g., where HF is removed prior to distillation. HF may be removed fromthe halogenated hydrocarbon components of the product mixture usingconventional aqueous solution scrubbing techniques. However, theproduction of substantial amounts of scrubbing discharge can createaqueous waste disposal concerns. Thus, there remains a need forprocesses utilizing HF in such product mixtures.

While the initial mixture treated in accordance with the presentinvention can be obtained from a variety of sources, including by addingHFC-338pcc to HF-containing compositions, an advantageous use of theinstant invention resides in treating the effluent mixtures from thepreparation of HFC-338pcc as described above. Generally, the reactioneffluents have a molar ratio of HF:HFC-338pcc from about 0.1:1 to about100:1. The preferred HF:HFC-338pcc molar ratio is from about 1:1 to 10:1for vapor phase fluorination reactions and about 1:1 to about 50:1 forliquid phase reactions. The most preferred HF:HFC-338pcc molar ratio isfrom about 2:1 to 5:1 to achieve maximum benefit from the instantprocess. When the initial mixture treated in accordance with theinvention also contains HCl and other low-boilers (e.g., CHF₂ CF₂ CF₂CF₃), the HCl and other low-boilers are removed in another distillationcolumn before feeding the mixture to the azeotrope separation columns.

High-boilers, if present, can be removed in an independent distilationcolumn after separation of HF from HFC-338pcc.

FIG. 1 is illustrative of one method of practicing this invention.Referring to FIG. 1, a feed mixture, derived from an HCFC-338pccsynthesis reactor, comprising HF and HFC-338pcc, wherein the molar ratioof HF:HFC-338pcc is greater than about 3:1, preferably greater thanabout 4:1, from an HCl removal column (not shown), is passed throughline (426) to a multiple stage distillation column (410) operating at atemperature of about 100° C. and a pressure of about 1480 kPa. Thebottoms of the distillation column (410) which contains HF at atemperature of about 115° C. and a pressure of about 1500 kPa is removedthrough line (436) and can be recycled back to the HFC-338pcc synthesisreactor. The distillate from column (410) which contains HF/HFC-338pccazeotrope (HF:HFC-338pcc molar ratio is about 3:1) is removed from thetop of the column (410) and sent through line (435) to column (420). Thedistillate from column (420) which contains HF/HFC-338pcc azeotrope(HF:HFC-338pcc molar ratio is about 7:1) and is at a temperature ofabout 20° C. and a pressure of about 140 kPa is removed from the top ofcolumn (420) and is recycled through line (445) to column (410). Thebottoms of the distillation column (420) which contain essentially pureHFC-338pcc at about 57° C. and 156 kPa is removed from the bottom of thecolumn (420) through line (446). In this embodiment column (410)operates as a high pressure column. Column (420) operates as a lowpressure column.

In another embodiment of this invention the pressures of the columns arereversed. Again referring to FIG. 1, a feed mixture, derived from anHFC-338pcc synthesis reactor, wherein the HF:HFC-338pcc molar ratio inthe feed mixture is about 3:1 or less, from an HCl removal column (notshown), is passed through line (426) to a multiple stage distillationcolumn (410), operating at a temperature of about 20° C. and a pressureof about 140 kPa. The bottoms of the distillation column (410) whichcontain essentially pure HFC-338pcc at a temperature of about 57° C. andand a pressure of about 156 kPa is removed from the bottom of column(410) through line (436). The distillate from column (410) whichcontains HF/HFC-338pcc azeotrope (HF:HFC-338pcc molar ratio is about7:1) at a temperature of about 20° C. and a pressure of about 140 kPa isremoved from the top of column (410) and sent through line (435) tocolumn (420). The distillate from column (420) which containsHF/HFC-338pcc azeotrope (HF:HFC-338pcc molar ratio is about 3:1) and isat a temperature of about 100° C. and a pressure of about 1480 kPa isremoved from the top of column (420) and is recycled through line (445)to column (410). The bottoms of the distillation column (420) whichcontain HF at a temperature of about 115° C. and a pressure of about1500 kPa is removed through line (446) and can be recycled back to theHFC-338pcc synthesis reactor. In this embodiment column (410) operatesas a low pressure column. Column (420) operates as a high pressurecolumn.

While specific temperatures, pressures and molar ratios were recited inthe above two embodiments, variation of the pressure will also causeshifts in the HF:HFC-338pcc molar ratios and in the distillationtemperatures. The use of a "low" and a "high" pressure column in tandemas described above can be used to separate HF from HFC-338pcc for anyHF:HFC-338pcc ratio (e.g., from 0.1:1 to 100:1).

Those skilled in the art will recognize that since the drawings arerepresentational, it will be necessary to include further items ofequipment in an actual commercial plant, such as pressure andtemperature sensors, pressure relief and control valves, compressors,pumps, storage tanks and the like. The provision of such ancillary itemsof equipment would be in accordance with conventional chemicalengineering practice.

The distillation equipment and its associated feed lines, effluent linesand associated units should be constructed of materials resistant tohydrogen fluoride, hydrogen chloride and chlorine. Typical materials ofconstruction, well-known to the fluorination art, include stainlesssteels, in particular of the austenitic type, and the well-known highnickel alloys, such as Monel® nickel-copper alloys, Hastelloy®nickel-based alloys and, Inconel® nickel-chromium alloys. Also suitablefor reactor fabrication are such polymeric plastics aspolytrifluoro-chloroethylene and polytetrafluoroethylene, generally usedas linings.

Without further elaboration, it is believed that one skilled in the artcan, using the description herein, utilize the present invention to itsfullest extent. The following preferred specific embodiments are,therefore, to be construed as merely illustrative, and does notconstrain the remainder of the disclosure in any way whatsoever.

EXAMPLES Examples 1 to 5 and Comparative Examples A and B Hydrogenolysisof HCFC-328lcc to HCFC-338pcc in the Presence of HF

Legend

HCFC-328lcc or 328lcc is CHF₂ CF₂ CF₂ CClF₂

HFC-338pcc or 338pcc is CHF₂ CF₂ CF₂ CHF₂

HP is high pressure.

LP is low pressure.

The carbon support used in the examples was a 4×8 mesh (about 4.7 mm×2.4mm) commercial grade coconut shell carbon which had (before washing) anash content of about 2.6 weight percent. After hydrochloric acidwashing, the carbon support had an ash content of less than about 0.1weight percent.

Liquid HCFC-328lcc (analysis: 93.3% 328lcc and 6.7% unknowns), 3mL/hour, was vaporized and mixed with 20 cc/minute of hydrogen andeither 0, 5 or 10 mL/minute of HF. This vapor mixture was sent through a0.5" (12.7 mm) O.D.×8" (203 mm) Hastelloy® nickel alloy reactor containg5.0 g of 0.5 weight percent palladium supported on acid-washed carbonmaintained at the various temperatures shown in Table 1 using afluidized sand bath. Only a small portion of the total reactor effluentwas sent to the gas chromatograph for organic product analysis. The bulkof the product stream which also contains inorganic acids such as HCland HF was sent to a caustic scrubber for neutralization of the acids. Asample of the product stream was analyzed using gas chromatography.Results of these in analysis, in area % are shown in Table 1.

                  TABLE 1                                                         ______________________________________                                              Temp.    HF       Unknowns 3281 cc                                                                             338 ppc                                Ex.   °C.                                                                             mL/min.  area %   area %                                                                              area %                                 ______________________________________                                        FEED  --       --       6.7      93.3   0.0                                   1     200       5       4.5      74.3  21.1                                   2     200      10       4.0      75.3  20.7                                   A     200      --       4.8      74.9  20.3                                   3     250      10       5.7       9.8  84.5                                   B     250      --       5.4      10.4  84.3                                   4     275      10       8.2       0.6  91.2                                   5     300      10       9.8       0.0  90.2                                   ______________________________________                                    

Examples 6 and 7

In the following two examples, all values for the compounds are in molesand temperatures are in Celsius. The data were obtained by calculationusing measured and calculated thermodynamic properties. The numbers atthe top of the columns refer to FIG. 1.

    ______________________________________                                        EXAMPLE 6                                                                             426      435      436    445     446                                          Feed     HP Col.  Recycle                                                                              HF/338 pcc                                                                            338 pcc                              Compound                                                                              Mixture  Dist.    HF     Recycle Prod.                                ______________________________________                                        HF      83.3     86.5     83.3   86.5    --                                   338 pcc 16.7     28.7     0.08   12.1    16.6                                 Temp. °C.                                                                      102      102      115    22      57                                   Press. kPa                                                                            1480     1480     1500   136     156                                  ______________________________________                                        EXAMPLE 7                                                                             426      435      436    445     446                                          Feed     LP Col.  338 pcc                                                                              HP Col. Recycle                              Compound                                                                              Mixture  Dist.    Prod.  Dist.   HF                                   ______________________________________                                        HF      33.3     57.3     --     23.9    33.3                                 338 pcc 16.7     8.0      16.6   7.9     0.08                                 Temp. °C.                                                                      22       22       22     102     115                                  Press. kPa                                                                            136      136      136    1480    1500                                 ______________________________________                                    

What is claimed is:
 1. A process for producing1,1,2,2,3,3,4,4-octafluorobutane, comprising:(a) reacting a mixturecomprising 2,2,3,3-tetrafluorobutane and chlorine to form a mixture ofchloro-compounds selected from the group consisting of CCl₃ (CF₂)₂ CCl₃,CHCl₂ (CF₂)₂ CCl₃, CH₂ Cl(CF₂)₂ CCl₃, CH₃ (CF₂)₂ CCl₃, CH₃ (CF₂)₂ CHCl₂and CH₃ (CF₂)₂ CH₂ Cl wherein compounds of the formula C₄ H_(x) Cl_(6-x)F₄, where x is 0 or 1, comprise at least about 50 mole % of said mixtureof chloro-compounds; (b) contacting a mixture comprising compounds ofthe formula C₄ H_(x) Cl_(6-x) F₄ from (a) and hydrogen fluoride with afluorination catalyst to form a mixture of fluoro-compounds selectedfrom the group consisting of CCl₂ F(CF₂)₂ CCl₃, CCl₂ F(CF₂)₂ CCl₂ F,CCl₂ F(CF₂)₂ CClF₂, CClF₂ (CF₂)₂ CClF₂, CClF₂ (CF₂)₂ CF₃, CHCl₂ (CF₂)₂CCl₂ F, CHClF(CF₂)₂ CCl₃, CHCl₂ (CF₂)₂ CClF₂, CHClF(CF₂)₂ CCl₂ F, CHF₂(CF₂)₂ CCl₃, CHClF(CF₂)₂ CClF₂, CHF₂ (CF₂)₂ CCl₂ F, CHCl₂ (CF₂)₂ CF₃,CHClF(CF₂)₂ CF₃, CHF₂ (CF₂)₂ CClF₂ and CHF₂ (CF₂)₂ CF₃ wherein compoundsof the formula C₄ H_(2-y) Cl_(y) F₈, where y is 1 or 2, comprise atleast about 10 mole % of said mixture of fluoro-compounds; and (c)contacting a mixture comprising compounds of the formula C₄ H_(2-y)Cl_(y) F₈ from (b) and hydrogen with a hydrogenolysis catalyst toproduce CHF₂ CF₂ CF₂ CHF₂ ; sufficient chloro-compounds formed in (a)being recycled to the chlorination of (a) and sufficientfluoro-compounds formed in (b) being recycled to the chlorination of (a)or the fluorination of (b) to provide a selectivity to CHF₂ CF₂ CF₂ CHF₂of at least about 75% based upon the moles of CH₃ CF₂ CF₂ CH₃ reacted in(a).
 2. A process for the purification of CHF₂ CF₂ CF₂ CHF₂ from amixture comprising HF and CHF₂ CF₂ CF₂ CHF₂ produced by the process ofclaim 1, comprising(a) subjecting the mixture of HF and CHF₂ CF₂ CF₂CHF₂ to a distillation step in which a composition enriched in either(i) HF or (ii) CHF₂ CF₂ CF₂ CHF₂ is removed as a first distillate withthe bottoms being enriched in the other of said components (i) or (ii);(b) subjecting said first distillate to an additional distillationconducted at a different pressure in which the component enriched asbottoms in (a) is removed as a second distillate with the bottoms of theadditional distillation enriched in the components enriched in the firstdistillate; and (c) recovering said CHF₂ CF₂ CF₂ CHF₂ essentially freeof HF as bottoms from either the distillation of step (a) or thedistillation of step (b).
 3. The process of claim 2 wherein said mixtureconsists essentially of hydrogen fluoride in combination with aneffective amount of CHF₂ CF₂ CF₂ CHF₂ to form an azeotrope orazeotrope-like composition with hydrogen fluoride, said azeotropiccomposition containing from about 3.5 to 36.8 mole percent CHF₂ CF₂ CF₂CHF₂.
 4. A compound selected from the group consisting of CCl₂ FCF₂ CF₂CClF₂, CCl₃ CF₂ CF₂ CCl₂ F, CHCl₂ CF₂ CF₂ CCl₃, CHCl₂ CF₂ CF₂ CCl₂ F,CHClFCF₂ CF₂ CCl₃, CHCl₂ CF₂ CF₂ CClF₂, CHClFCF₂ CF₂ CCl₂ F, CHF₂ CF₂CF₂ CCl₃, CHF₂ CF₂ CF₂ CCl₂ F, CHClFCF₂ CF₂ CF₃, CH₃ CF₂ CF₂ CH₂ Cl andCH₂ ClCF₂ CF₂ CCl₃.
 5. The compound of claim 4 which is CCl₂ FCF₂ CF₂CClF₂.
 6. The compound of claim 4 which is CCl₃ CF₂ CF₂ CCl₂ F.
 7. Thecompound of claim 4 which is CHCl₂ CF₂ CF₂ CCl₃.
 8. The compound ofclaim 4 which is CHCl₂ CF₂ CF₂ CCl₂ F.
 9. The compound of claim 4 whichis CHClFCF₂ CF₂ CCl₃.
 10. The compound of claim 4 which is CHCl₂ CF₂ CF₂CClF₂.
 11. The compound of claim 4 which is CHClFCF₂ CF₂ CCl₂ F.
 12. Thecompound of claim 4 which is CHF₂ CF₂ CF₂ CCl₃.
 13. The compound ofclaim 4 which is CHF₂ CF₂ CF₂ CCl₂ F.
 14. The compound of claim 4 whichis CHClFCF₂ CF₂ CF₃.
 15. The compound of claim 4 which is CH₃ CF₂ CF₂CH₂ Cl.
 16. The compound of claim 4 which is CH₂ ClCF₂ CF₂ CCl₃.